We propose and realize a substrate-free metal-cavity surface-emitting microlaser with both top and sidewall metal and a bottom distributed Bragg reflector as the cavity structure. The transfer-matrix method is used to design the laser structure based on the round-trip resonance condition inside the cavity. The laser is in diameter and in height, and operates at room temperature with continuous-wave mode. Flip-bonding the device to a silicon substrate with a conductive metal provides efficient heat removal. A high characteristic temperature about 425 K is observed from 10 to .

We report the coupling between surface plasmons and dipole-localized surface plasmons in a composite hole-patch structure at terahertz frequencies. The coupling is found to be changed by increasing the inner patch size, which causes prominent resonance frequency shift in the enhanced transmission. The experimental results show good agreement with numerical simulation. The study clarifies well the nature of coupling between surface plasmons and dipole-localized surface plasmons and is thus of help to identify the role of surface plasmons in the enhanced transmission observed in subwavelength metallic structures.

We report the development of a GaN-based green light-emitting diode(LED) with a selective area photonic crystal (SPC) structure, which was formed outside the -bonding electrode on -GaN. As a result, the optical output power of LEDs with SPC was enhanced by 78% compared to that without PC. In addition, the forward voltage, series resistance, and leakage current of LEDs with SPC were remarkably improved. These results show that the light extraction efficiency of green LEDs can be greatly increased using the SPC structure, with no degradation of electrical properties.

High absorption efficiency is particularly desirable at present for various microtechnological applications including microbolometers, photodectors, coherent thermal emitters, and solar cells. Here we report the design, characterization, and experimental demonstration of an ultrathin, wide-angle, subwavelength high performance metamaterial absorber for optical frequencies. Experimental results show that an absorption peak of 88% is achieved at the wavelength of , though theoretical results give near perfect absorption.

Catastrophic optical damage (COD) is analyzed during single current pulse excitation of 975 nm emitting diode lasers. Power transients and thermal images are monitored during each pulse. The COD process is unambiguously related to the occurrence of a “thermal flash” of Planck’s radiation. We observe COD to ignite multiple times in subsequent pulses. Thermography allows for tracing a spatial motion of the COD site on the front facet of the devices. The time constant of power decay after the onset of COD has values from 400 to 2000 ns, i.e., an order of magnitude longer than observed for shorter-wavelength devices.

III-V microtubes and nanotubes are formed by a strain-induced self-rolling process. We report room-temperature photoluminescence(PL) characteristics of such microtubes with embedded GaAs quantum-well structures and wall thickness as thin as 38 nm. Rolled-up tubes show dramatic PL intensity enhancement compared to their planar counterparts. Holey tubes, formed using patterned membranes, display further increase in intensity implying better light extraction efficiency with the air holes. Systematic shift of PL peak position as a function of tube curvature, attributed to strain induced band structure change, is established.

We report on the characterization and performance of epitaxialstructures and photodiodes based on InAs/GaSb type-II superlatticesgrown by metalorganic chemical vapor deposition. Interfacial layers were introduced at the superlatticeinterfaces to compensate the tensile strain and hence to improve the overall material quality of the superlatticestructures. The optimal morphology and low strain was achieved via a combined interfacial layer scheme with layers. Using this scheme, a photodiodestructure with a 360-period InAs/GaSb superlattice was grown on a GaSb substrate, which operates at 78 K with a cut-off wavelength of and a peak responsivity of 0.6 A/W at .

We present a deformable mirror that is composed by a metalized membrane with a monolithic nonpixelated photoconductive substrate. The assembly constitutes a continuous photocontrolled deformable mirror and is driven through suitable light intensity distributions illuminating the photoconductive element. The continuous deformation of the reflective surface provides an all-optical and dynamical control of the incoming wave front, without spatial segmentation and with a deformation as large as a few microns.

A high-sensitivity thermal sensing is demonstrated by coating a layer of polydimethylsiloxane(PDMS) on the surface of a silica toroidal microresonator on a silicon wafer. Possessing high-whispering gallery modes(WGMs), the PDMS-coated microresonator is highly sensitive to the temperature change in the surroundings. We find that, when the PDMS layer becomes thicker, the WGM experiences a transition from redshift to blueshift with temperature increasing due to the negative thermal-optic coefficient of PDMS. The measured sensitivity (0.151 nm/K) is one order of magnitude higher than pure silicamicrocavity sensors. The ultrahigh resolution of the thermal sensor is also analyzed to reach .

We use photoemission microscopy to characterize localized surface plasmon distributions in nanostructured gold layers on indium-tin-oxide/glass substrates. The Aufilms have a fractal dimension of and smallest feature sizes of . We use femtosecond laser pulses at a wavelength of for the plasmon excitation. Photoelectron emission occurs by a three-photon process in localized areas of indium-tin-oxide with diameter. In these areas the photoemission rate is enhanced several thousand fold compared to nonstructured surface areas. The results show that plasmon enhanced photoemission can be induced in a nonabsorbing material in proximity to a plasmon-active metalnanostructure.

Electromagneticband gap (EBG) structures have interesting properties in terms of electromagnetic wave propagation. Using a plasma discharge in an EBG structure may increase its reconfigurability. The use of microplasma arrays in the design of EBG structures is however complex and may cause energy losses. In this paper, we show through experiments and simulations that EBG effects can be obtained in structures where a single discharge plasma is used to create a defect in a periodic structure of metallic rods.

An efficient scheme of acceleration and collimation of dense plasma is proposed and examined. In the scheme, a target placed in a cavity coupled with a guiding channel is irradiated by a laser beam introduced into the cavity through a hole and accelerated along the channel by the pressure of the ablating plasma confined in the cavity. Using , 0.3 ns laser pulse of energy up to 200 J and a thin CH target, it was shown that the energetic efficiency of acceleration in this scheme is an order of magnitude higher than in the case of conventional ablative acceleration.

We report the values of steps of heat capacity during the glass transition in a variety of metallic glasses (MGs). It is found that is around and almost invariable for the MGs. Based on the Eyring’s theory [N. Hirai and H. Eyring, J. Polym. Sci.37, 51 (1959)], the phenomenon corresponds to a critical reduced free volume value. This exhibits that the glass transition takes place when the reduced free volume approaches to in the MG systems. The value, consistent with that of the yielding of MGs, confirms that temperature and stress are equivalent for fluidizing MGs. Our results give an implication to understanding the glass transition in MGs as a Lindemann-type melting behavior [F. A. Lindemann, Z. Phys.11, 609 (1910)].

The dynamics of exciton coupling to photons and LO-phonons in a three-level quantum-dot system is studied using the Wigner–Weisskopf approach. An analytical solution to the system for a rectangular driving pulse is derived, and the wave function of an exciton is found to form a unit vector directed to the surface of an Bloch hemisphere. For long decoherence times, the vector traces out a temperature (T)-dependent Rabi circle with increase pulse area. An increase in T does not deform the Rabi circle but shrinks its radius. Accordingly, a diverse representational scheme is proposed. These properties expand scenarios to T-dependent regimes.

A study of InGaN/GaN multiple layer quantum dot(QD) structures with varying barrier thicknesses is reported. With increasing barrier thickness both a redshift in the photoluminescence(PL) peak energy and increase in the PL decay lifetime is observed. This is attributed to an increase in the size of the internal electric field and the influence on the electronic structure via the quantum confined Stark effect. Theoretical surface integral potential calculations support this interpretation. A minimum barrier thickness of 4 nm appears to be required for the formation of separate homogeneous QD layers.

The appearance of carrier traps and the deactivation of dopants are typical hydrogen-related phenomena that are of prime importance to the reliability of traditional Si-based devices. Here we probe with first-principles calculations, the dynamics of hydrogen as individual impurities or in complexes with dopants in strained Si (s-Si) and SiGe systems. We find that the charged state determines the tendency of hydrogen to be released from dopant sites and to shuttle between a SiGe substrate and a s-Si overlayer. In this way, the effect of hydrogen differs between accumulation and inversion cycles of s-Si and SiGe devices.

The integration of InGaN quantum dots into GaN-based monolithic microcavitiesgrown by metal-organic vapor-phase epitaxy is demonstrated. Microphotoluminescencespectra reveal distinct spectrally sharp emission lines around 2.73 eV, which can be attributed to the emission of single InGaN quantum dots. The samples are structured into airpost pillar microcavities. The longitudinal and transversal mode spectra of these cavities are in good agreement with theoretical calculations based on a vectorial transfer-matrix method. Quality factors up to have been achieved.

The graphenenanosheet (GNS)/ultrahigh molecular weight polyethylene composite with a two-dimensional conductive network of GNSs exhibits an increasing positive temperature coefficient (PTC) of resistivity while thermally treated at a certain temperature. This anomalous phenomenon is originated from the reduced viscosity of polymer matrix, crystallization induced local flow and weak interactions among the overlapping joints of GNSs, which allow GNSs to migrate to the polymer matrix, thus weakening the conductive paths and increasing the PTC intensity. A facile approach is accordingly developed to prepare a conductivepolymercomposite with a tunable PTC intensity.

GaNquantum dotsdoped with Tm atoms and embedded in AlN have been characterized by high-angle annular dark-field imaging using a scanning transmission electron microscope. Direct visualization of individual Tm atoms in AlN layers has been achieved. We have found that besides being present in GaNdots, Tm atoms also tend to segregate at AlN barriers. The Tm distribution is related to the capping mechanism of the dots with AlN. A visibility coefficient based on locally integrated, rather than peak, intensities is introduced to determine quantitatively the number of Tm atoms in a given atomic column. Experimental and simulated images show that this visibility presents a reduced sensitivity to the defocus or to the position of the Tm atom within the thin lamella.